1. Field of the Invention
The present invention generally relates to the design, manufacture and assembly of electrical generation equipment. More particularly, the present invention relates to a method for assembly of a generator stator.
2. Description of the Prior Art
An operational generator comprises a stator including a frame and a core, a rotor, at least one coil winding, and a coupling for coupling the generator to a turning gear or turbine.
The generator stator core is the largest single component in the train of a turbine generator set. Traditionally, stator cores have been manufactured from thousands of laminations of relatively thin steel plates which are stacked, pressed and clamped together into the shape of the stator core (e.g., a large cylindrical form). Clamping is necessary to maintain the geometric form of the stator core and to withstand electromagnetic forces imposed on the stator core during generator operation. Improperly clamped laminations may result in plate vibration during generator operation, which results from magnetic impulses or core elliptical dilation. Moreover, air space between the laminations may lead to high thermal resistance and decreased cooling efficiency. Fillers are often inserted into the stack of plates to compensate for voids caused by plate crown. Additionally, the fillers ensure that the clamping pressure is evenly distributed over the full plate area.
Typically, the stator core is assembled from the steel plates directly at the final manufacturing assembly site. However, the large size of the stator core and the need for proper clamping results in stator core manufacturing difficulties, including generous floor space and high crane requirements. Traditionally, two assembly procedures have been employed to form the cylindrical shaped stator core. In one procedure, the steel plates are stacked directly in a stator frame; in the other procedure, the steel plates are first stacked and clamped in an external stacking fixture. The complete stator core is then lifted into the stator frame via a large crane.
The manufacture of stator cores via the traditional methods results in manufacturing lead time and other associated manufacturing difficulties. For example, if the core is stacked directly in the stator frame, the frame must be delivered to the assembly site before any manufacturing steps can occur. Additionally, intermediate core pressing equipment is needed to press and clamp the steel plates together at incremental lengths. If, on the other hand, the stator core is manufactured in an external fixture, the frame does not have to arrive on site before the manufacturing; however, the external fixture itself adds to the manufacturing costs and requires additional floor space on site. Moreover, the external fixture method requires a heavy duty crane of sufficient height to lift the assembled core into the stator frame. In either traditional manufacturing procedure, the core stacking process requires several days to complete.
In addition to assembly complications, stator cores assembled according to traditional methods may experience operational problems. Such cores have a tendency to settle or relax during service. To help alleviate this tendency, various consolidation techniques and high clamping forces are required during assembly, further increasing the assembly time and costs. Moreover, heavy structural members are required at the core ends to hold the laminations in place, and access for future retightening may be required.
It is also desirable to minimize the costs associated with manufacturing the components necessary to assemble a generator on-site. Production of an excessive volume of generator components can result in increased storage costs and product waste. Thus, there is a need to better control inventory of generator components to reduce manufacturing and storage costs associated with excessive volume production.
Therefore, a need still exists for an improved method for assembling an operational stator in the field or other location.